All projections to do with IoT have been in 'telephone numbers'. Variously, analysts have projected numbers of connected IoT devices growing to as few as 30 billion, and as many as 75 billion devices world-wide by 2020.

In the past I have generally found analysts tend to overestimate emerging market sizes. But it all becomes very real when you see €11b of cellular telecoms revenue in the last calendar year driven off the back of the IoT roll-out.

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IoT revenue topped €11bn for operators in 2016
03 February 2017
Research from Berg Insight found number of M2M connections grew by 30% to 398m
Mobile operators raised more than €11 billion in revenues from the Internet of Things (IoT), according to research from Berg Insight, with 398 million cellular machine-to-machine connections in use by the end of the year.
In 2015, M2M revenues were €6.7 billion, according to the Swedish analysts.
IoT generated as much as €200 million in quarterly sales for operators such as Vodafone and Verizon, with analysts Berg predicting a handful of operators will generate more than €1 billion in revenue from IoT connectivity, solutions and applications next year.